A. Technical Field
The present invention relates to a catalyst and a process for removing organohalogen compounds such as dioxins.
B. Background Art
Exhaust gases from incineration facilities for disposing of industrial wastes and city wastes contain trace amounts of poisonous organohalogen compounds such as dioxins, PCB and chlorophenols. Particularly, the dioxins are extremely poisonous even in very small quantities and have a serious influence on human bodies. Therefore, a technology for removing the dioxins is desired to be developed as quickly as possible.
Generally, the organohalogen compounds are chemically extremely stable. Particularly, the dioxins are substances so difficult to decompose that they are said to semipermanently remain in the world of nature. In addition, because their contents in the exhaust gases are very small, it is difficult to efficiently remove them with conventional catalysts for disposing of exhaust gases.
In consideration of these circumstances, the present applicant verified that a catalyst comprising titanium oxide was fundamentally effective, and then the applicant found that decomposition reactions of organohalogen compounds could be promoted by well diffusing dilute components of exhaust gases by improving physical properties, specifically, pore diameter distribution, and further, pore volume, of the above catalyst. On the basis of this finding, the present applicant developed the undermentioned two kinds of catalysts to file a patent application thereof (Japanese Patent Application No. 09-358146).
1) A catalyst for removing organohalogen compounds, which comprises titanium oxide and vanadium oxide as catalytic components, and has pores that includes a group of pores having a pore diameter distribution peak in the range of 0.01 to 0.05 μm and another group of pores having a pore diameter distribution peak in the range of 0.1 to 0.8 μm.
2) A catalyst for removing organohalogen compounds, which comprises titanium oxide, a titanium-silicon composite oxide, and vanadium oxide as catalytic components, and has pores that includes a group of pores having a pore diameter distribution peak in the range of 0.01 to 0.05 μm and another group of pores having a pore diameter distribution peak in the range of 0.8 to 4 μm.
These catalysts have excellent removability, but it is preferable that a catalyst for removing organohalogen compounds, which exhibits higher performances than those catalysts, appears.